Now showing 1 - 10 of 66
  • Publication
    ROCK activity and the Gβγ complex mediate chemotactic migration of mouse bone marrow-derived stromal cells
    Bone marrow-derived stromal cells (BMSCs), also known as mesenchymal stem cells, are the focus of intensive efforts worldwide to elucidate their function and biology. Despite the importance of BMSC migration for their potential therapeutic uses, the mechanisms and signalling governing stem cell migration are still not fully elucidated. Methods: We investigated and detailed the effects of MCP-1 activation on BMSCs by using inhibitors of G protein-coupled receptor alpha beta (GPCR αβ), ROCK (Rho-associated, coiled-coil containing protein kinase), and PI3 kinase (PI3K). The effects of MCP-1 stimulation on intracellular signalling cascades were characterised by using immunoblotting and immunofluorescence. The effectors of MCP-1-mediated migration were investigated by using migration assays (both two-dimensional and three-dimensional) in combination with inhibitors. Results: We established the kinetics of the MCP-1-activated signalling cascade and show that this cascade correlates with cell surface re-localisation of chemokine (C motif) receptor 2 (CCR2) (the MCP-1 receptor) to the cell periphery following MCP-1 stimulation. We show that MCP-1-initiated signalling is dependent on the activation of βγ subunits from the GPCR αβγ complex. In addition, we characterise a novel role for PI3Kγ signalling for the activation of both PAK and ERK following MCP-1 stimulation. We present evidence that the Gβγ complex is responsible for PI3K/Akt, PAK, and ERK signalling induced by MCP-1 in BMSCs. Importantly, we found that, in BMSCs, inhibition of ROCK significantly inhibits MCP-1-induced chemotactic migration, in contrast to previous reports in other systems.Conclusions: Our results indicate differential chemotactic signalling in mouse BMSCs, which has important implications for the translation of in vivo mouse model findings into human trials. We identified novel components and interactions activated by MCP-1-mediated signalling, which are important for stem cell migration. This work has identified additional potential therapeutic targets that could be manipulated to improve BMSC delivery and homing.
      318Scopus© Citations 14
  • Publication
    Stabilization of C-RAF:KSR1 complex by DiRas3 reduces availability of C-RAF for dimerization with B-RAF
    RAF family kinases are central components of the Ras-RAF-MEK-ERK cascade. Dimerization is a key mechanism of RAF activation in response to physiological, pathological and pharmacological signals. It is mediated by a dimer interface region in the RAF kinase domain that is also conserved in KSR, a scaffolding protein that binds RAF, MEK and ERK. The regulation of RAF dimerization is incompletely understood. Especially little is known about the molecular mechanism involved in the selection of the dimerization partner. Previously, we reported that Ras-dependent binding of the tumour suppressor DiRas3 to C-RAF inhibits the C-RAF:B-RAF heterodimerization. Here we show that DiRas3 binds to KSR1 independently of its interaction with activated Ras and RAF. Our data also suggest that depending on the local stoichiometry between DiRas3 and oncogenic Ras, DiRas3 can either enhance homodimerization of KSR1 or recruit KSR1 to the Ras:C-RAF complex and thereby reduce the availability of C-RAF for binding to B-RAF. This mechanism, which is shared between A-RAF and C-RAF, may be involved in the regulation of Ras12V-induced cell transformation by DiRas3.
    Scopus© Citations 6  527
  • Publication
    The spatiotemporal regulation of RAS signalling
    (Portland Press, 2016-10-19) ; ;
    Nearly 30% of human tumours harbour mutations in RAS family members. Post-translational modifications and the localisation of RAS within subcellular compartments affect RAS interactions with regulator, effector and scaffolding proteins. New insights into the control of spatiotemporal RAS signalling reveal that activation kinetics and subcellular compartmentalisation are tightly coupled to the generation of specific biological outcomes. Computational modelling can help utilising these insights for the identification of new targets and design of new therapeutic approaches.
    Scopus© Citations 17  407
  • Publication
    The APC network regulates the removal of mutated cells from colonic crypts
    Self-renewal is essential for multicellular organisms but carries the risk of somatic mutations that can lead to cancer, which is particularly critical for rapidly renewing tissues in a highly mutagenic environment such as the intestinal epithelium. Using computational modeling and in vivo experimentation, we have analyzed how adenomatous polyposis coli (APC) mutations and β-catenin aberrations affect the maintenance of mutant cells in colonic crypts. The increasing abundance of APC along the crypt axis forms a gradient of cellular adhesion that causes more proliferative cells to accelerate their movement toward the top of the crypt, where they are shed into the lumen. Thus, the normal crypt can efficiently eliminate β-catenin mutant cells, whereas APC mutations favor retention. Together, the molecular design of the APC/β-catenin signaling network integrates cell proliferation and migration dynamics to translate intracellular signal processing and protein gradients along the crypt into intercellular interactions and whole-crypt physiological or pathological behavior.
    Scopus© Citations 16  289
  • Publication
    Integrating network reconstruction with mechanistic modeling to predict cancer therapies
    (American Association for the Advancement of Science, 2016-11-22) ; ; ;
    Signal transduction networks (STNs) are often rewired in cancerous cells. Effective cancer treatment requires identifying and repairing these harmful alterations. We developed a computational framework which can identify these aberrations and predict potential targets for intervention. It reconstructs network models of STNs from noisy and incomplete perturbation response data, and then uses the reconstructed networks to develop mechanistic models of STNs for predicting potential treatments. As a proof of principle, we analysed a perturbation dataset targeting Epidermal Growth Factor Receptor (EGFR) and Insulin like 2 Growth Factor 1 Receptor (IGF1R) pathways in a panel of colorectal cancer (CRC) cells, revealing cell line specific STN rewiring. Specifically, we found that the feedback inhibition of IRS1 by p70S6K is associated with resistance to EGF receptor (EGFR) inhibition, and disrupting this feedback may restore sensitivity to EGFR inhibitors in CRC cells. These findings were experimentally validated in vitro and in zebrafish (Danio rerio) xenografts.
    Scopus© Citations 49  686
  • Publication
    Crosstalk and Signaling Switches in Mitogen-Activated Protein Kinase Cascades
    Mitogen-activated protein kinase (MAPK) cascades control cell fate decisions, such as proliferation, differentiation, and apoptosis by integrating and processing intra- and extracellular cues. However, similar MAPK kinetic profiles can be associated with opposing cellular decisions depending on cell type, signal strength, and dynamics. This implies that signaling by each individual MAPK cascade has to be considered in the context of the entire MAPK network. Here, we develop a dynamic model of feedback and crosstalk for the three major MAPK cascades; extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38), c-Jun N-terminal kinase (JNK), and also include input from protein kinase B (AKT) signaling. Focusing on the bistable activation characteristics of the JNK pathway, this model explains how pathway crosstalk harmonizes different MAPK responses resulting in pivotal cell fate decisions. We show that JNK can switch from a transient to sustained activity due to multiple positive feedback loops. Once activated, positive feedback locks JNK in a highly active state and promotes cell death. The switch is modulated by the ERK, p38, and AKT pathways. ERK activation enhances the dual specificity phosphatase (DUSP) mediated dephosphorylation of JNK and shifts the threshold of the apoptotic switch to higher inputs. Activation of p38 restores the threshold by inhibiting ERK activity via the PP1 or PP2A phosphatases. Finally, AKT activation inhibits the JNK positive feedback, thus abrogating the apoptotic switch and allowing only proliferative signaling. Our model facilitates understanding of how cancerous deregulations disturb MAPK signal processing and provides explanations for certain drug resistances. We highlight a critical role of DUSP1 and DUSP2 expression patterns in facilitating the switching of JNK activity and show how oncogene induced ERK hyperactivity prevents the normal apoptotic switch explaining the failure of certain drugs to induce apoptosis.
    Scopus© Citations 134  373
  • Publication
    Proteasomal down-regulation of the proapoptotic MST2 pathway contributes to BRAF inhibitor resistance in melanoma
    The RAS-RAF-MEK-ERK pathway is hyperactivated in most malignant melanomas, and mutations in BRAF or NRAS account for most of these cases. BRAF inhibitors (BRAFi) are highly efficient for treating patients with BRAFV600E mutations, but tumours frequently acquire resistance within a few months. Multiple resistance mechanisms have been identified, due to mutations or network adaptations that revive ERK signalling. We have previously shown that RAF proteins inhibit the MST2 proapoptotic pathway in a kinase-independent fashion. Here, we have investigated the role of the MST2 pathway in mediating resistance to BRAFi. We show that the BRAFV600E mutant protein, but not the wild-type BRAF protein, binds to MST2 inhibiting its proapoptotic signalling. Down-regulation of MST2 reduces BRAFi-induced apoptosis. In BRAFi-resistant cell lines, MST2 pathway proteins are down-regulated by ubiquitination and subsequent proteasomal degradation rendering cells refractory to MST2 pathway–induced apoptosis. Restoration of apoptosis can be achieved by increasing MST2 pathway protein expression using proteasome inhibitors. In summary, we show that the MST2 pathway plays a role in the acquisition of BRAFi resistance in melanoma.
      20Scopus© Citations 2
  • Publication
    Signalling mechanisms regulating phenotypic changes in breast cancer cells
    In MCF-7 breast cancer cells epidermal growth factor (EGF) induces cell proliferation, whereas heregulin (HRG)/neuregulin (NRG) induces irreversible phenotypic changes accompanied by lipid accumulation. Although these changes in breast cancer cells resemble processes that take place in the tissue, there is no understanding of signalling mechanisms regulating it. To identify molecular mechanisms mediating this cell-fate decision process, we applied different perturbations to pathways activated by these growth factors. The results demonstrate that phosphoinositide 3 (PI3) kinase (PI3K) and mammalian target of rapamycin (mTOR) complex (mTORC)1 activation is necessary for lipid accumulation that can also be induced by insulin, whereas stimulation of the extracellular-signal-regulated kinase (ERK) pathway is surprisingly dispensable. Interestingly, insulin exposure, as short as 4 h, was sufficient for triggering the lipid accumulation, whereas much longer treatment with HRG was required for achieving similar cellular response. Further, activation patterns of ATP citratelyase (ACLY), an enzyme playing a central role in linking glycolytic and lipogenic pathways, suggest that lipids accumulated within cells are produced de novo rather than absorbed from the environment. In the present study, we demonstrate that PI3K pathway regulates phenotypic changes in breast cancer cells, whereas signal intensity and duration is crucial for cell fate decisions and commitment. Our findings reveal that MCF-7 cell fate decisions are controlled by a network of positive and negative regulators of both signalling and metabolic pathways.
    Scopus© Citations 9  345
  • Publication
    A-Raf
    (Nature Publishing Group, 2010-04-06) ;
    A-Raf (v-raf murine sarcoma 3611 viral oncogene homolog) is a serine/threonine protein kinase of the Raf family that comprises A-Raf, B-Raf and C-Raf. Raf kinases are at the apex of the three-tiered Raf-MEK-ERK/MAPK pathway that features over 150 substrates and regulates many fundamental cellular functions, including proliferation, differentiation, transformation, apoptosis and metabolism. The only commonly accepted substrates for all three Raf kinases are MEK1/2, a pair of dual-specificity kinases that have ERK1/2 as substrates. A-Raf is the least studied member of the Raf family. A-Raf seems to be regulated similarly to C-Raf, with binding to activated Ras initiating the growth-factor-induced activation of A-Raf. In addition, A-Raf activity is regulated by phosphorylation, lipid interactions and protein-protein interactions. For instance, binding of the regulatory subunit of casein kinase II, CK2β, was shown to enhance A-Raf kinase activity. However, A-Raf is a poor MEK kinase with barely measurable catalytic activity, suggesting that A-Raf could have functions outside the MAPK cascade. A-Raf binding to mitochondrial membrane proteins suggests a potential role in mitochondrial transport and anti-apoptotic signaling pathways. Furthermore, the association of A-Raf with the pyruvate kinase M2, M2-PK, causing dimerization and inactivation of M2-PK, may link A-Raf signaling with energy metabolism and the Warburg effect in tumor cells. The generation of A-Raf knock-out mice revealed a role in neuronal migration and development. Recently, alternative A-Raf splice forms encoding truncated A-Raf proteins were identified. Owing to their ability to bind and block activated Ras, they function as physiological dominant-negative Ras inhibitors with roles in differentiation and transformation. A-Raf is expressed in most tissues, but expression levels differ dramatically. Elevated levels were reported in a number of malignancies, although no oncogenic mutations have been found.
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  • Publication
    Scopus© Citations 22  455